1. Field of the Invention
The present invention relates to a zoom lens, or a zoom lens barrel, which is provided with a cam mechanism using bottomed cam grooves formed on an inner peripheral surface of a cam barrel. At least one movable lens group is moved in the direction of the optical axis of the photographic optical system in a predetermined manner in accordance with the profiles of the bottomed cam grooves by rotation of the cam barrel.
2. Description of the Related Art
A zoom lens having a cam mechanism which uses bottomed cam grooves formed on an inner peripheral surface of a cam barrel so that one or more movable lens groups guided in the direction of the optical axis of the photographic optical system (i.e., in the optical axis direction) without rotating about the optical axis are moved in a predetermined manner by rotation of the cam barrel to obtain a continuously variable focal length is known in the art. In such a cam mechanism using bottomed cam grooves, if each cam follower pin formed on a lens frame is fitted in the zoom section (an operational section for varying the focal length) of the corresponding bottomed cam groove with a predetermined amount of play, the lens group supported by the lens frame may be eccentric and/or tilt relative to the optical axis. This deteriorates the optical performance of the zoom lens.
Such eccentricity or tilt of the lens group causes substantial problems, especially in a zoom lens of a digital camera, because object images are formed on the sensitive surface of a small CCD (CCD image sensor) which is much smaller than the picture plane of conventional cameras using light sensitive film. Namely, upon assembly, every lens element of a digital camera must be optically centered, correctly spaced, and held firmly with a relatively high precision ten times greater than that required in conventional cameras using light-sensitive film. For instance, if the angle of view is constant, the focal length of a photographing lens becomes shorter as the size of the picture plane reduces, which in turn reduces the sizes of all the elements of the photographing lens such as lens elements, and lens frames. Therefore, an influence that a tolerance (e.g., 10 xcexcm) has on the photographing lens system of a digital camera is much larger than an influence that the same tolerance has on the photographing lens system of a conventional camera using light-sensitive film. Accordingly, manufacturing error which falls within tolerance in the optical performance in the photographing optical system of a conventional camera using light-sensitive film can be out of tolerance in optical performance in the photographing optical system of a digital camera. Specifically in the photographic lens system of a digital camera, influence that eccentricity or tilt of a lens group relative to the optical axis has on the optical performance of the photographic lens system is larger than influence that a deviation of the same lens group from the original position in the optical axis direction.
To prevent such eccentricity and tilt from occurring, a mechanism for removing play between the cam follower pins and the bottomed cam grooves in which the cam followers are respectively fitted with resilient supports which support the cam follower pins has been proposed. The resilient supports become resiliently deformed in a radial direction to bias the cam follower pins against the bottomed cam grooves, respectively, to thereby remove the play between the cam follower pins and the bottomed cam grooves, so that each cam follower pin follows along the corresponding bottomed cam groove with a sufficient frictional resistance being generated therebetween.
However, according to such a play removing mechanism, if the resilient supports remain resiliently deformed over the long term, the resilient bias (i.e., the resilient biasing force) of each resilient support gradually becomes weak, which may deteriorate the performance of the mechanism.
Another problem present in a zoom lens having a cam mechanism using bottomed cam grooves, is that although each bottomed cam groove is provided with a leading section provided for leading each corresponding cam follower pin from the cam follower insertion opening of the bottomed cam groove, which is formed on the cam barrel, to the zoom section of the bottomed cam groove (which is provided for moving the lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with rotation of the cam barrel) ease of assembling and disassembling the zoom lens deteriorates if each cam follower is biased against not only a portion of the bottomed cam groove, which is used during operation of the zoom lens, but also another portion of the bottomed cam groove which is not used during operation of the zoom lens since the cam mechanism cannot be assembled or disassembled smoothly due to the frictional force generated between the cam follower pins and the bottomed cam grooves.
The present invention has been devise in view of the above-mentioned problems, and accordingly, an object of the present invention is to provide a zoom lens having a cam mechanism which reliably prevents eccentricity and tilt of a lens group relative to the optical axis from occurring during operation of the zoom lens while maintaining the performance of the prevention of lens eccentricity and tilt over a long term.
Another object of the present invention is to provide a zoom lens having a cam mechanism which reliably prevents eccentricity and tilt of a lens group relative to the optical axis from occurring during operation of the zoom lens and which excels in ease of assembly and disassembly the zoom lens.
To achieve the object mentioned above, according to an aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; bottomed cam grooves formed on an inner peripheral surface of the cam barrel; a lens frame guided in an optical axis direction; cam followers which project radially from the lens frame to be respectively engaged with the bottomed cam grooves; and resilient supports which respectively support the cam followers, each of the resilient supports being resiliently deformable in a radial direction, a resilient bias of each of the resilient supports causing each of the cam followers to be biased against a corresponding bottomed cam groove of the bottomed cam grooves. Each bottomed cam groove includes a zoom section for moving the lens frame between a telephoto position and a wide-angle position thereof in the optical axis direction in accordance with a rotational movement of the cam barrel; and an accommodation section for moving the lens frame to an accommodation position thereof, wherein a photographic operation is not performed. Each bottomed cam groove is formed so that a depth of the accommodation section is greater than a depth of the zoom section in the radial direction of the cam barrel. The resilient bias of each of the resilient supports causes each of the cam followers to be biased against each of the bottomed cam grooves wherein the follower pins are respectively fitted in the bottomed cam grooves so that no play exists when each of the bottomed cam grooves is positioned in the zoom section, and each of the resilient supports is free from being elastically deformed in the radial direction so that the cam followers are respectively inserted in the bottomed cam grooves with a predetermined amount of play when each of the bottomed cam grooves is positioned in the accommodation section.
In the bottomed cam grooves includes a first set of bottomed cam grooves having same profiles and a second set of bottomed cam grooves having same profiles, the profiles of the second set of bottomed cam grooves being different from the profiles of the first set of bottomed cam grooves. The lens frame includes a first lens frame and a second lens frame. The cam followers include a first set of cam followers which are provided on the first lens frame and a second set of cam followers which are provided on the second lens frame. The first set of cam followers are respectively engaged with the first set of bottomed cam grooves, and the second set of cam followers are respectively engaged with the second set of bottomed cam grooves. The resilient supports include a first set of resilient supports which resiliently support the first set of cam followers, and a second set of resilient supports which resiliently support the second set of cam followers. Each bottomed cam groove of the first set of bottomed cam grooves and the second set of bottomed cam grooves is formed so that the depth of the accommodation section is greater than the depth of the zoom section in the radial direction of the cam barrel.
Preferably, the zoom sections of each bottomed cam groove of the first set of bottomed cam grooves and each corresponding bottomed cam groove of the second set of bottomed cam grooves are formed on the inner peripheral surface of the cam barrel in the same range in a circumferential direction of the cam barrel.
Preferably, three of each of the cam followers, the bottomed cam grooves, and the resilient supports are provided at an equi-angular distance about the optical axis.
In an embodiment, the zoom section and the accommodation section of each of the bottomed cam grooves respectively includes a bottom surface; and a pair of opposing tapered side surfaces connected to the bottom surface, the pair of tapered side surfaces being respectively tapered so as to diverge away from each other as the pair of tapered side surfaces extend away from the bottom surface.
Preferably, a width of the bottom surface in the zoom section and a width of the bottom surface in the accommodation section are the same.
In an embodiment, the zoom lens further includes a linear guide barrel which is associated with the lens frame to guide the lens frame in the optical axis direction.
Preferably, the linear guide barrel is positioned inside the cam barrel and includes linear guide through-slots extending parallel to the optical axis; wherein the resilient supports include guide projections which are fitted in the linear guide through-slots from the inside of the linear guide barrel, respectively, so that the resilient supports are resiliently deformable inwards in the radial direction; and the cam followers project from the guide projections outwards in the radial direction to be respectively fitted in the bottomed cam grooves.
Preferably, the linear guide barrel and the can barrel are connected to each other to be relatively immovable in the optical axis direction and relatively rotatable about the optical axis.
Preferably, the resilient supports are formed integrally with the lens frame so that each of the resilient supports can be resiliently deformed in the radial direction.
The above-described zoom lens can be incorporated in a digital camera.
According to another aspect of the present invention, a zoom lens is provided, including a linear guide barrel, guided in an optical axis direction without rotating about the optical axis, having linear guide through-slots which extend parallel to the optical axis; a cam barrel fitted on the linear guide barrel to be immovable in the optical axis direction relative to the linear guide barrel and rotatable about the optical axis relative to the linear guide barrel, the cam barrel having bottomed cam grooves which are formed on an inner peripheral surface of the cam barrel; a lens frame having cam followers which are respectively engaged with the bottomed cam grooves, and guide projections which are respectively engaged with the linear guide through-slots; and resilient supports formed on the lens frame to support the cam followers, respectively, each of the resilient supports being resiliently deformable radially, a resilient bias of each of the resilient supports causing each of the cam followers to be biased against a corresponding bottomed cam groove of the bottomed cam grooves. Each of the bottomed cam grooves includes a zoom section for moving the lens frame, in the optical axis direction, between a telephoto position and a wide-angle position thereof in accordance with rotation of the cam barrel; and an accommodation section for moving the lens frame to an accommodation position thereof, wherein a photographic operation is not performed. Each of the bottomed cam grooves is formed so that a depth of the accommodation section is greater than a depth of the zoom section in a radial direction of the cam barrel. The resilient bias of each of the resilient supports causes each of the cam followers to be biased against each of the bottomed cam grooves wherein the follower pins are respectively fitted in the bottomed cam grooves so that no play occurs when each of the bottomed cam grooves is positioned in the zoom section. Each of the resilient supports is free from being elastically deformed in the radial direction so that the cam followers are respectively inserted in the bottomed cam grooves with a predetermined amount of play when each of the bottomed cam grooves is positioned in the accommodation section.
According to another aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; bottomed cam grooves formed on an inner peripheral surface of the cam barrel; a lens frame guided in an optical axis direction; cam followers which project radially from the lens frame to be respectively engaged with the bottomed cam grooves; and resilient supports which respectively support the cam followers, each of the resilient supports being resiliently deformable in a radial direction, a resilient bias of each of the resilient supports causing each of the cam followers to be biased against a corresponding bottomed cam groove of the bottomed cam grooves. Each of the bottomed cam grooves includes a deep groove portion, so that each of the resilient supports is free from being elastically deformed in the radial direction so that the cam followers are respectively inserted in the bottomed cam grooves with a predetermined amount of play when each of the bottomed cam grooves is positioned in the deep groove portion. The deep groove portion includes at least a part of an assembly section of each of the bottomed cam grooves, through which a corresponding cam follower of the cam followers passes only during assembly of the zoom lens.
In an embodiment, each of the bottomed cam grooves further includes a normal-depth groove portion whose depth is smaller than a depth of the deep groove portion in the radial direction, so that, when each of the cam followers is positioned in the normal-depth groove portion, the resilient bias of each of the resilient supports causes each of the cam followers to be biased against each of the bottomed cam grooves wherein the follower pins are respectively fitted in the bottomed cam grooves with no play. The normal-depth groove portion includes a zoom section for moving the lens frame between a telephoto position and a wide-angle position thereof in the optical axis direction in accordance with rotation of the cam barrel.
In an embodiment, the deep groove portion includes a leading section for leading the corresponding cam follower from a cam follower insertion opening, which is open at one end of the cam barrel, to the normal-depth groove portion. Each of the bottomed cam grooves includes a shallow groove portion in the middle of the leading section, and a depth of the shallow groove portion is smaller than a depth of the normal-depth groove portion in the radial direction of the cam barrel.
Preferably, three of each of the cam followers, the bottomed cam grooves, and the resilient supports are provided at an equi-angular distance about the optical axis.
In an embodiment, the normal-depth groove portion and the deep groove portion of each bottomed cam grooves respectively includes a bottom surface; and a pair of opposing tapered side surfaces connected to the bottom surface, the pair of tapered side surfaces being respectively tapered so as to diverge away from each other as the pair of tapered side surfaces extend away from the bottom surface.
Preferably, a width of the bottom surface in the normal-depth groove portion and a width of the bottom surface in the deep groove portion are the same.
According to another aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; first bottomed cam grooves formed on an inner peripheral surface of the cam barrel; second bottomed cam grooves formed on the inner peripheral surface of the cam barrel and having different profiles from the first bottomed cam grooves; a first lens frame having first cam followers which are respectively engaged with the first bottomed cam grooves; a second lens frame having second cam followers which are respectively engaged with the second bottomed cam grooves; and a linear guide barrel which is associated with the first lens frame and the second lens frame to guide the first lens frame and the second lens frame in an optical axis direction. Each of the first bottomed cam grooves includes a first zoom section for moving the first lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with rotation of the cam barrel; a first leading section for leading corresponding one of the first cam followers from a first cam follower insertion opening, which is open at one end of the cam barrel, toward the first zoom section; and a terminal section positioned on the opposite side of the first zoom section with respect to the first leading section. Each of the first leading section and the terminal section is formed as a first deep groove portion used only during assembly of the zoom lens, a depth of the first deep groove portion being greater than a depth of the first zoom section in a radial direction of the cam barrel. Each of the second bottomed cam grooves includes a second zoom section for moving the second lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with rotation of the cam barrel; and a second leading section for leading corresponding one of the second cam followers from a second cam follower insertion opening which is open at the one end of the cam barrel, toward the second zoom section. The second leading section is formed as a second deep groove portion used during assembly of the zoom lens, a depth of the second deep groove portion being greater than a depth of the second zoom section in the radial direction of the cam barrel. The terminal section and the second cam follower insertion opening are formed at the same circumferential position in a circumferential direction of the cam barrel. Upon assembly of the first lens frame and the second lens frame to the cam barrel and the linear guide barrel, the first cam followers are respectively inserted into the first leading sections via the first cam follower insertion openings, the linear guide barrel and the cam barrel are rotated relative to each other until the first cam followers reaches respective the terminal section of corresponding one of the first bottomed cam grooves, and subsequently, the second cam followers are respectively inserted into the second leading sections via the second cam follower insertion openings.
Preferably, the leading section includes a shallow groove portion in the middle of the second leading section; and a depth of the shallow groove portion is smaller than a depth of the second zoom section in the radial direction of the cam barrel.
In an embodiment, each of the first bottomed cam grooves includes a first connecting section positioned between the first zoom section and the terminal section, through which a corresponding cam follower of the first cam followers passes only during assembly of the zoom lens, wherein a depth of the first connecting section is the same as the depth of the first zoom section in the radial direction. The first cam follower can be held in the terminal section of the first bottomed cam groove, due to the difference of depth between the terminal section and the connecting section.
In an embodiment, each of the second bottomed cam grooves includes a second connecting section positioned between the second zoom section and the second leading section, through which a corresponding cam follower of the second cam followers passes only during assembly of the zoom lens, wherein a depth of the second connecting section is the same as the depth of the second zoom section in the radial direction. The second cam follower can be held in the leading section of the second bottomed cam groove, due to the difference of depth between the leading section and the connecting section.
In an embodiment, the zoom lens further includes first resilient supports which respectively support the first cam followers, each of the first resilient supports being resiliently deformable in the radial direction, a resilient bias of each of the first resilient supports causing each of the first cam followers to be biased against a corresponding bottomed cam groove of the first bottomed cam grooves; and second resilient supports which respectively support the second cam followers, each of the second resilient supports being resiliently deformable in the radial direction, a resilient bias of each of the second resilient supports causing each of the second cam followers to be biased against a corresponding bottomed cam groove of the second bottomed cam grooves. The first follower pins are respectively fitted in the first zoom section of the first bottomed cam grooves so that no play occurs during zooming, due to a resilient bias of the first resilient supports which are elastically deformed in the radial direction. The second follower pins are respectively fitted in the second zoom section of the second bottomed cam grooves so that no play occurs during zooming, due to a resilient bias of the second resilient supports which are elastically deformed in the radial direction. The first follower pins are respectively inserted in the first leading section with a predetermined amount of play and the terminal section of the first bottomed cam grooves, so that each of the first resilient supports is free from being elastically deformed in the radial direction. The second follower pins are respectively inserted in the second leading section of the second bottomed cam grooves with a predetermined amount of play, so that each of the second resilient supports is free from being elastically deformed in the radial direction.
Preferably, the linear guide barrel and the cam barrel are connected to each other to be relatively immovable in the optical axis direction and relatively rotatable about the optical axis.
The above-described zoom lens can be incorporated in a digital camera.
The present disclosure relates to subject matter contained in Japanese Patent Applications Nos. 2000-23842 and 2000-23843 (both filed on Feb. 1, 2000) which are expressly incorporated herein by reference in their entireties.